Warning system



Oct. 10, 1961 F. SULLIVAN ETAL WARNING SYSTEM Filed March 9, 1959 Fig.1

Heaeriel Safiimn Samuel Edward Eaton INVENTORS.

Agent United States Patent 3,003,349 WARNING SYSTEM Frederick Sullivan, North Wilmington, and Samuel Edward Eaton, Hingham, Mass., assignors to Arthur D. Little, Inc., Cambridge, Mass., a corporation of Massachusetts Filed Mar. 9, 1959, Ser. No. 798,171 12 Claims. (Cl. 7340.7)

This invention relates to warning or alarm systems adapted to provide to the human senses a warning of leakage of radioactive materials, especially from closed systems, or of the hazardous presence of such materials.

Radioactive materials such as cesium 137, cobalt 60, strontium 90, and the like are customarily encased within one or a plurality of hermetically sealed covers or laminae of stainless steel, glass, noble metal, or other suitable material, in order that they may be contained safely'and without danger to personnel or contamination of surrounding materials by direct contact. The radioactive material, which may be solid, liquid or gaseous, may be formed and covered or protected in one or another of several ways, although in present practice it is frequently a solid in the shape of a long, narrow rod and the covering or cladding is in the form of a thin-walled cylindrical container, or of a plurality of such containers which nest together closely, one within the other. Each of these is hermetically closed against the escape of the radioactive material. The thus clad or encased radioactive material (hereinafter usually referred to as an element) when in use is ordinarily placed within shielding means which may be in the form of a suitable solid with an aperture in which the element is placed, or is submerged in water or other suitable liquid. The danger of escaping radioactive material from the elements is, however, a constant problem, especially where instrumentation is not common.

As is well known, radioactive materials have a rapidly increasing use, not only for military purposes, but especially for industrial purposes, such as for fuel elements, in thickness and other gauges, and as radiation processing sources for sterilizing, etc.

Furthermore, there is the problem. of safe disposal of radioactive wastes. Such increasing uses and applications of these radioactive materials emphasize the need for the safe handling and for the rapid detection of radiation hazards resulting from leaks through the cladding or containers. Such leaks are presently detected by wipe tests and by monitoring counters which are installed in most laboratories which now handle these materials. However, the absence of such instrumentation, failure of detection equipment, or the handling of the radioactive elements by untrained personnel emphasizes the need for a simple, rapid warning system capable of triggering a sensory response which will warn personnel of possible danger from or leakage of radioactive material from an element containing it. Although the cladding is ordinarily designed and arranged to be hermetically sealed so that no radioactive material will escape, there is always danger due, for example, to the highly active and/or corrosive nature of the radioactive material, or to any error, hazards or damage in handling, that leaks will develop through cladding whereby portions of the radioactive material will escape. This is especially true in the case of radioactive materials which are not in the form of a mas sive solid, but are rather in gaseous, liquid, or powder form it is a principal object of this invention to provide at detecting means associated with the radioactive elements whereby any leakage becomes immediately manifested. It is a further object of this invention to provide such detecting means in the form of a substance which is placed either between the respective layers of cladding or within the innermost such layer, either surrounding or mixed with the radioactive material itself. A further object of this invention is to provide such detecting means which will not be damaged by radiation from the radioactive material and which can be detected by one or more suitable means such as by odor, by appearance, or by the automatic actuating of detecting means. Other objects will appear as the description proceeds. I I

This invention will now be described in more detail with reference to the accompanying drawings Wheri11- FIG. 1 represents a fuel element or other clad radioactive material positioned within a solid shield;

FIG. 2 represents a longitudinal cross-section of atypical element of this invention;

FIG. 3 represents an enlarged cross-section of a portion of an element of this invention; and

FIG. 4 represents another modification of this invention.

The arrangement shown in FIG. 1 of the drawings is that of a shield 10 having a cylindrical aperture or orifice 12 in which is placed a fuel element 14 or other radioactive source. Details of a typical element 14 are shown in FIG. 2 wherein the radioactive material is represented by the numeral16 and the cladding or claddings by the numeral 18. The cladding 18 may be a single layer.

I FIG. 3 shows an enlarged detail of a portion of an element'of the general type of FIG. 2. In this instance, several cladding layers are shown, identified by the numerals 20, 22, 24, and 26. A warning material 21in accordance with the present invention, is placed between two contiguous layersofthe cladding, in this instance between layers 20 and 22. Alternatively or in addition, the warning material of this invention may be mixed with the radioactive material 16 or may surround the same between it and the inner cladding 20. It is also possible to use different types of warning materials in the same element, e.g. by placing one of them between any two contiguous layers of cladding and another between any other two contiguous layers.

When the warning material between claddings, as at 29 in FIG. 3 is gaseous, the claddings between which it is placed may be spaced apart by suitable means such as lugs 28, and the gas may also be under pressure in order to promote its rapid diffusion in the event of a leak.

FIG. 4 shows another modification wherein a warning material 30,- typically a fluorescent warning material, is placed as a coating over the surface 32; of a container 34 within which radioactive material is sealed.

The warning material, if intended to be detected because of its odor, should, of course, be non-hazardous to personnel and environment and should be unique (i.e. not like other odors in the environment concerned), persistent, pungent, not significantly damaged by radiation from the radioactive material (although it may be altered, as indicated below), and not injurious to that material. It must be capable of alerting people to immediate action to correct the hazard. Selection should take into account the consideration that radiation-stable materials usually have low molecular weights or a ringtype aromatic structure. Radiation stability can be ascertained experimentally by exposing the warning materials to intense doses of radiation of the type to be warned against. Suitable warning materials for the purposes of this invention also include those which are not in themselves notably detectable or distinguishable by the senses, but which are converted promptly thereto upon exposure to the type of radiation to be detected hereby. Suitablewarning materials also include those which are not radiation-stable, but which may be reformed into suitable form upon leakage out of, and away from, the radioactive element. For example, chlorine gas is not very radiation-stable, being dissodated into chlorine atoms or ions by radiation. Yet,

upon removal from a radiation field, chlorine would again be formed; or hydrogen chloride 'or other chlorine compound from reaction with the surrounding air or moisture might be produced as the warning medium. Odorants of the class referre'dto above are the thinalcohols (mercaptans) and tlzlioeth'ers, certain cyclic sulfur-bearing compounds, and various'lachrymators and irritants, as illustrated below. The cyclic sulfur compounds are especially stable and resistant to thermalv breakdown at temperatures as high as 500",'C. and

' more. Mercaptans have exceedingly low thresholds of detection (approximately 3.3)(10 ppm.) and are of such character that any leakage into the surrounding atmosphere is at once detected. Typical ofsuch mercaptans are methyl, ethyl and propyl mercaptarr and lower homologues thereof, lower mercapto-alcohols such as Z-mercapto ethanol, and other compounds typically containing the -SH radical. Examples ofthioethers, which have the generic formula RS'R', are 'diethyl sulfide, allyl sulfide, and mixed sulfides, where R and R are different radicals. Among the above-mentioned cyclic sulfur compounds are .thiophene, while other odorous sulfur compounds within the class are allylisothiocyanate and dimethyl trithiocarbonate. Choice will [depend both upon the factors recited above, and upon phenone, and crotonaldehyde (which both lachrymator.

and irritant). Phenyl isothiocyanate is an example of an irritant. V

Many other odorous compounds may serve as warning materials, including various nitrogen-containing and/or unsaturated hydrocarbon compounds such as pyridine, dinitrobenzene, indene, indole and vinyl cyclohexane.

In instances where the warning material has inadequate stability in the presence of the radiation to be warned against, a stabilizer may be added. Such stabilizers are for example aromatic compounds such as benzene, diphenyl, and terphenyl. 7

Another type of warning material which is particularly useful in instances where the radioactive material is in submerged position is one which provides a visual alarm such as a fluorescent compound or a visible dye either of which would be released into the liquid medium surrounding the radioactive material, ejg. asin a swimming pool type of system. The fluorescent compound may be one which would be detectable in the presence of a suitable light source arranged to shine continuously upon the liquid medium. Alternatively, the fluorescent compound may be one which fluoresces when activated by the radiation from the source itself.

The visual warning material may also be used in instances where the radioactive material is'not submerged, e.g. in the form of a colored liquid material such as a non-volatile dye dissolved in a suitable solvent. Development of a leak in the container would allow the colored warning material to seep out and remain visible on the elements surface as positive evidence of leakage. A slight pressure to force the warning agent out of the leak may be maintained in the element 'by incorporating a gas such as air with the agent, or selecting an agent "which exhibits a slight decomposition to a gas upon irradiation.

A coating 30 (FIG. 4) may advantageously serve to warn of the dangers of radiation from the radioactive material enclosed within an element, even though there severe if not fatal'radiation damage to any individual maybe no leakage. Thus, such an element unless properly shielded (e.g. by shield 10, FIG. 1) can cause who is near it or who handles it without proper precautions. However, such an element does not ordinarly look any different from any. other non-radiating object of the same size and external structure. But, by providing a suitable coating '30 which glows in the presence of radiation item the contained radioactive material, any individual who sees the resulting glowing object is effectively warned that the object is not a conventional and safe one. Suitable fluorescent materials for this purpose are the television tube and fluorescent light phosphors, such as calcium lead silicate and magnesium tungstate. Organic fluorescent materia'rs such as the sodium salt of fluorescein may alsobe used.

The fluorescent coating 30 may advantageously be made up of the above-described fluorescent warning material in a vehicle which does not afliect the action of either the warning materialor the radioactivity, and which is unaffected thereby, and which is adherent to the surface 32 of the objectjcoated. Many ordinary lacquers, e.g. of the phenolic type, are suitable for this purpose. The warning material is dissolved or dispersed in the vehicle and theresulting composition applied in the vmanner appropriate for the vehicle. used.

Alternatively, in connection with the arrangement shown in FIG. 4, the coating 30 maybe a fluorescent material which serves to detect the presence of dangerous radiation from sources adjacent to, but outside or", container 34. p I

Obviously, the warning'materials' of this "invention may be used in conjunction with the Geiger counters and other like detecting means presently used for instrumental warning purposes. It is also clear that the warning material of this invention must not interfere with the action or effectiveness of the radioactive material. The radiation from the latter may in some uses be relatively weak, and obviously the warning material employed should be chosen accordingly, with respect to characteristics, quantity and location.

It should also be noted that the placement of the warning material of this invention outside of the innermost cladding, as at 29 of FIG. 2, will serve to warn of potential leakage of radioactive material before active leakage occurs, ininstances where the outer claddings have been ruptured or broken, but the innermost cladding is still intact. V I

Other warning materials detectable by the human senses, and other means for detecting radioactivity thereby, will occur to those skilled in this art, within the scope of the appended claims.

What is claimed is: V

1. A sealed radioactive element consisting of'a radioactive material and a casing completely surrounding said material, and a warning medium. associated with said element and positioned within said casing, said medium being adapted to move outwardly from within said casing through any break therein and thereupon to provide a warning, directly detachable by the human senses, of the presence or potential leakage of radioactivity, said are dium being confined within said casing in the absence or such break. V

2. A 'seaie'd radioactive element according to. claim 1 wherein said medium is under superatmospheric pressure. 3. A sealed radioactive element according to claim 1 wherein said medium contains a substance adapted to stabilize it against deleterious efiects of said radioactivity. V H

4. A sealed radioactive element according to claim 1 wherein said medium is a fluorescent compound.

5. A sealed radioactive element according to claim 1 wherein said medium is a lachrymator.

6. A sealed radioactive element according to claim 1 wherein said medium is a dye.

7. A sealed radioactive element according to claim '1 wherein said medium is an odorant which is non-toxic, persistent or pungent.

8. A sealed radioactive element according to claim 7 wherein said odorant is a mercaptan.

9. A sealed radioactive element according to claim 7 wherein said odorant is a cyclic sulfur compound.

10. A sealed radioactive element according to claim 7 wherein said odorant is an irritant.

11. A sealed radioactive element consisting of radioactive material encased within a plurality of successive superposed layers of cladding, and a Warning medium positioned in said element within at least the outer of said layers, said medium being adapted to diffuse outwardly from said element through any break in said outer layer, but being otherwise confined within said 15 2,878,392

References Cited in the file of this patent UNITED STATES PATENTS 243,741 Tudor July 5, 1881 339,206 Phelan Apr. 6, 1886 2,096,099 Gaugler Oct. 19, 1937 2,518,327 Jahn Aug. 8, 1950 2,844,735 Crevtz July 22, 1958 2,846,872 McAdams Aug. 12, 1958 Polito Mar. 17, 1959 Patent No. 3. 003349 UNITED STATES PATENT. OFFICE CERTIFICATE OF CORRECTION October 10 1961 Frederick Sullivan et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4 line 58 for "detachable" read detectable Signed and sealed this 27th day-of March 1962.

(S EAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

